Node.js extension of GeoJSON that encodes topology

 node-topojson is an extension of GeoJSON that encodes topology. Rather than
 representing geometries discretely, geometries in TopoJSON files are stitched
 together from shared line segments called *arcs*. TopoJSON eliminates
 redundancy, offering much more compact representations of geometry than with
 GeoJSON; typical TopoJSON files are 80% smaller than their GeoJSON
 equivalents. In addition, TopoJSON facilitates applications that use topology.